Comparison Characteristics Of Weathering Degree,Clay Minerals And Iron Oxides Of Carbonate Weathering Crusts At Different Altitude In West Yunnan-Guizhou Plateau

It is not clear whether the widely distributed red weathering crust on the Yunnan-Guizhou Plateau is the product of modern climate or the product of paleoclimate before the plateau uplift.In order to explore this problem in depth,the western region of the Yunnan-Guizhou Plateau with the most complete vertical climatic zone spectrum is selected as the study area.The chemical weathering degree,clay minerals and iron oxide characteristics of carbonate weathering crusts at different altitude are studied,and the following research results show:(1)The results of geochemical element analysis show that SiO₂/Al₂O₃,SiO₂/Fe₂O₃,SiO₂/Al₂O₃+Fe₂O₃,weathering leaching coefficient(ba),A index and B index,chemical alteration index(CIA),A/NK,A/CNK,Rb/Sr of weathering crusts at different altitude are inconsistent,indicating the weathering crusts at different altitude are not formed in the same climate environment.The chemical weathering degree at different altitudes reflected by the chemical weathering index parameters is consistent with the theoretical chemical weathering degree calculated from the modern climate,which indicates that the formation of these weathering crusts are affected by the modern three-dimensional climate environment.(2)The results of clay mineral identification show that the content of gibbsite(in total clay minerals)is significantly different at different altitude,which indicates that the chemical weathering degrees of weathering crusts are not consistent at different altitude.The variation characteristics of the content of gibbsite with altitude are similar to those of modern three-dimensional climate,indicating that weathering crusts at different altitude are the products of modern three-dimensional climate environment.(3)The results of iron oxide identification show that the content of goethite(in total iron oxide minerals)increased gradually with the increase of altitude,whose relative content gradually increased from 8%to 52%.This result is consistent with the dry-wet condition of modern three-dimensional climate,indicating that weathering crusts are controlled by modern climate environment.(4)Through field observation and identification of geochemical elements,the remains of ancient weathering crusts whose weathering degree is not affected by modern three-dimensional climate are found at 2000-2400 m and>3200 m.It shows that although the formation of weathering crusts at different altitude on the Yunnan-Guizhou Plateau is mainly controlled by the modern three-dimensional climate,there are also a small amount of paleo-weathering crust residues reflecting the paleo-climatic environment before the plateau uplift.